Various vehicles such as long-haul trucks, boats and recreational vehicles are equipped with electrical and electronic equipment that require power when the vehicle is underway and when it is parked. Such devices are often referred to as “hotel loads,” and include heating and air conditioning, lighting, and appliances such as refrigerators, coffee makers and microwave ovens as well as television and entertainment systems. Although the vehicle engine can be left running at idle to provide power for hotel loads, the result is undesired fuel consumption, engine wear and the emission of pollutants. Thus, over the years, various arrangements have been proposed to supply power to vehicle hotel loads while the vehicle engine is not running.
Arrangements for powering hotel loads when the vehicle engine is not running fall into two basic categories: (1) auxiliary power units (APUs) or generator sets; and, (2) electrical power systems that are either powered by the vehicle batteries or are electrically connected to a conventional ac power outlet known as shore power. The arrangements of both categories overcome the need to idle the vehicle engine in order to power the vehicle hotel loads, thus reducing vehicle engine wear and fuel consumption. However, certain disadvantages and drawbacks remain with respect to both the currently available APUs and the currently available shore based electrical power systems.
The type of APU most commonly used is a motor-driven generator that utilizes diesel or other fuel such as gasoline or liquid petroleum. Such APUs provide an immediate source of electrical power for vehicle hotel loads and are capable of generating sufficient power for operating high demand devices such as conventionally designed heating and air conditioning units. However, APUs—especially those driven by diesel or gasoline engines—are noisy and expel pollutants into the atmosphere. Further, conventional APUs are relatively heavy, have a relatively high initial cost and present issues from the standpoint of maintenance costs and scheduling.
There are two types of electrical power systems for supplying power to vehicle hotel loads: (1) “shore power” systems in which the power system must be connected to an external source of conventional ac power (e.g., power supplied by a utility company); and, (2) systems that solely rely on the vehicle batteries. In some cases, vehicles are equipped with both types of systems.
Typically, a shore power system distributes power directly to ac powered hotel loads and includes an ac-to-dc converter for supplying current to dc powered hotel loads and for charging the vehicle batteries. Shore powered systems are superior to the use of an APU from the standpoint of initial cost, weight, maintenance considerations and noise. However, a conventional power outlet may not be available where the vehicle operator either needs to or is required to stop.
Systems that use the vehicle batteries to supply hotel loads primarily consist of wiring to interconnect dc powered hotel loads to the vehicle batteries and an inverter unit for transforming dc current drawn from the batteries to ac current for the ac powered hotel loads. Such systems also are superior to the use of an APU from the standpoint of initial cost, weight, maintenance considerations and noise. However, systems powered solely by the vehicle batteries often are not capable of supplying the needed amount of current for the vehicle hotel loads for a sufficient or desired period of time without discharging the vehicle batteries to a point at which the vehicle cannot be started. Thus, these systems often include monitoring circuits and alarms to guard against overly discharging the batteries.
Design constraints applicable to power systems for hotel loads are in part dictated by the vehicle in which the systems are employed. One very demanding situation is the design and implementation of such power systems for large long-haul trucks equipped with sleepers (e.g., Class 8 vehicles, which consist of trucks having a gross vehicle weight exceeding 33,000 pounds). Powering the hotel loads with the engine idling, or periodically starting the truck to charge the vehicle batteries during stops of any duration often is not a viable option. Specifically, a growing number of state and regional authorities are enacting “no-idle” rules and regulations that limit how often the engine may be idled during a stop and the duration over which the engine may be idled. On the other hand, Federal legislation mandates ten continuous hours rest during a 24-hour period for commercial truck drivers. No-idle regulations also complicate existing harsh design and operational constraints that apply to hotel load power systems for long-haul trucks. For example, a system for providing hotel power in long-haul trucks should be capable of operating reliably over a wide range of ambient temperatures (outside air temperature), such as 110° F. (approximately 42° C.) or more, to −20° F. (approximately −12° C.) or less. Reliable operation at sub-zero ambient temperatures can be difficult to achieve because the power capacity of the vehicle batteries is greatly reduced at low ambient temperatures. By way of example, the capacity of a typical lead-acid truck battery is reduced by approximately 50% relative to supplying a 5-amp load current when the ambient temperature reaches freezing. Thus, the time period during which hotel loads can be powered is dramatically reduced.
Regardless of ambient temperature, long-haul trucks require hotel load power for required driver rest periods of 10 hours or more while retaining adequate power to start a large diesel engine of the type that normally powers such a vehicle. In addition, it is desirable that the power system be capable of supplying hotel loads for a period of time that substantially exceeds a rest period of 10 hours. Specifically, reserve power capability is desired so that hotel load current can be supplied should the truck be unable to resume a trip because of extremely harsh weather conditions or other causes.
Although weight and maintenance considerations can be important with respect to other vehicles, they are of special significance with respect to power systems for long-haul trucks. Reduced weight means reduced fuel costs and less pollution and, in cases such as bulk transport vehicles, can mean increased load capacity. Low maintenance can mean shorter return on investment and, further, can result in additional saving if maintenance of the power system can be performed on the same schedule as other truck maintenance.
Although progress has been made, the prior art has not fulfilled the need a battery-powered low maintenance, low cost, light weight, efficient power system that provides reliable operation over a wide temperature range while simultaneously ensuring that electrical power is available for engine starting at low ambient temperatures and after extended periods of operation